This disclosure relates generally to improving the purity of water. More particularly, it relates to an apparatus and system for the purification of or desalination of water from underground. Still more particularly, this disclosure relates to a filtration apparatus and system that may be used to recover and purify water from a borehole in the earth.
Various types of filters can be employed to improve the quality of water taken from zones within the earth by removing suspended or dissolved substances from the water. For example, reverse osmosis (RO) membrane technology, is used to remove salt from brackish and saline water sources to produce fresh, purified water. The RO process requires high pressure pumping which consumes significant levels of energy. The RO process concentrates the salts from the feed water source into a more-concentrated stream that requires disposal. In a typical system, the pressure of saline/brackish feed water is boosted through a high pressure pump and delivered to a filter having an RO membrane. The pump increases the feed water pressure such that the forward pressure across the RO membrane exceeds the natural reverse osmotic pressure across the membrane. The reverse osmotic pressure is caused by the difference in salt concentration between a saline water on one side of the RO membrane and fresh water on the other side of the RO membrane. The reverse osmotic pressure acts to compel fresh water to go (or return) to the feed water side. However, when a pump is used to pressurize and feed the saline water to the membrane, the elevated pressure from the pump causes water molecules to pass through the membrane in opposition to reverse osmotic pressure and to arrive as permeate on the low pressure, fresh water side of the membrane. In this process salt molecules are retained on the high pressure side of the membrane along with a portion of the feed water, developing a concentrated reject stream that exits a concentrated fluid outlet of the filter. A pressure control device, such as a back-pressure regulator or back-pressure regulating valve, is coupled to the concentrated fluid outlet of the filter to allow the pump to develop pressure and to govern, or at least to influence, the flow rate from the concentrated fluid outlet. In this manner, the back-pressure regulator influences the recovery ratio, which is the ratio of the rate of recovery of permeate or purified water from the filter to the rate of supply of feed water to the filter.
For an oil well producing hydrocarbons, enhanced oil recovery can be achieved in some instances by injecting water into a second well or borehole generally near the producing oil well. The water is injected into the production zone or a zone that fluidically communicates with the production zone to increase the pore pressure in the production zone and cause an increased flow of hydrocarbons into the oil well.